Is this a miscarriage?

I calculated that my LMP was Nov 7. My first positive urine pregnancy that I took at the clinic was Dec 11. I went to the hospital last night because I had some scant brown discharge every time I wipe. No red or pink blood on the toilet paper. Just like old dark brown “blood” like when ur ending your period. I have no other symptoms then the usual nausea and headaches here and there. No cramps. No back pain. They did a transvaginal ultrasound and it showed a gestational sac measuring 0.9 cm with no yolk sac. So the gestational sac is empty. And the radiologist stated that it’s small. My hcg was 4,159 ( I have no baseline to compare it too). They asked me to come back in two days to do another hcg. What do you guys think? Is this a early sign of a miscarriage.